test/ring: reduce compilation time

test/ring: reduce compilation time

Rework test code to reduce code complexity for the compiler and
bring down compilation time and memory consumption.
Current test_ring_enqueue/test_ring_dequeue functions contain
too many branches and it takes compiler a lot of effort to resolve all
of them at compile time.
So the patch replaces these branchy function invocations
with an  array of function pointers (test_enqdeq_impl[]).
That way compiler knows straightway which function to use
for each particular case.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>